What kind of phone do you use? My father uses a 4 year old Samsung Galaxy S5 and he's currently experiencing sudden force stopping of the app, lagging, freezing, etc... He tells me that this happens after every update but usually gets better within a day or two. I don't really believe him, but I cleaned his phone as much as I can removing useless apps and data but it's still not working smoothly. Afterall this, I think it could be that the processor is too weak to handle PoGo, but I'm iffy because a Galaxy S5 still should work fairly well.
So maybe try deleting any unused apps, data, and useless files to free up space and help your phone run smoother? That that fails maybe just wait a day or two like my dad and see if it gets better.